linux-kernel - Re: [PATCH] backlight: pwm_bl: apply the initial backlight state with sane defaults

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Message-ID: <t6wtfnmnclnzwdpbmdcalvyf3mulmpexnryolxkygqkpx7vdwz@dqwbwvlzawrr>
Date: Fri, 7 Nov 2025 09:00:33 +0100
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Daniel Thompson <danielt@...nel.org>, Lee Jones <lee@...nel.org>
Cc: Michael Grzeschik <m.grzeschik@...gutronix.de>, 
	Jingoo Han <jingoohan1@...il.com>, Helge Deller <deller@....de>, 
	Pengutronix <kernel@...gutronix.de>, linux-pwm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: pwm_bl: apply the initial backlight state
 with sane defaults

On Thu, Oct 30, 2025 at 11:51:07AM +0000, Daniel Thompson wrote:
> On Thu, Jul 31, 2025 at 10:47:18AM +0200, Michael Grzeschik wrote:
> > Currently when calling pwm_apply_might_sleep in the probe routine
> > the pwm will be configured with an not fully defined state.
> >
> > The duty_cycle is not yet set in that moment. There is a final
> > backlight_update_status call that will have a properly setup state.
> > However this change in the backlight can create a short flicker if the
> > backlight was already preinitialised.
> >
> > We fix the flicker by moving the pwm_apply after the default duty_cycle
> > can be calculated.
> >
> > Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
> 
> Reviewed-by: Daniel Thompson (RISCstar) <danielt@...nel.org>

I guess this tag resulted in Lee picking up the change. I wonder if you
share my concern and who's responsibility it is now to address it.

Best regards
Uwe

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